Currently running some stress tests with JBoss6 (snapshots from 2010-12-15 currently) and perfromance looks very well.

But after the system is running for some time (12-24 hours), there occur transaction errors. One of them is targeted in HORNETQ-583 but another one seems to be a conflict between the EntitySynchronizationInterceptor and Arjuna, which occurs out of a sudden, without any difference in the executed processes, see stacktrace extract below, will also attach the whole log file.

java.lang.IllegalStateException: ARJUNA-16082 Synchronizations are not allowed! Transaction status isActionStatus.ABORTING
at com.arjuna.ats.internal.jta.transaction.arjunacore.TransactionImple.registerSynchronizationImple(TransactionImple.java:367)
at com.arjuna.ats.internal.jta.transaction.arjunacore.TransactionImple.registerSynchronization(TransactionImple.java:344)
at org.jboss.ejb.plugins.EntitySynchronizationInterceptor.register(EntitySynchronizationInterceptor.java:160)
at org.jboss.ejb.plugins.EntitySynchronizationInterceptor.invokeHome(EntitySynchronizationInterceptor.java:218)

java.lang.IllegalStateException: ARJUNA-16082 Synchronizations are not allowed! Transaction status isActionStatus.ABORTING at com.arjuna.ats.internal.jta.transaction.arjunacore.TransactionImple.registerSynchronizationImple(TransactionImple.java:367) at com.arjuna.ats.internal.jta.transaction.arjunacore.TransactionImple.registerSynchronization(TransactionImple.java:344) at org.jboss.ejb.plugins.EntitySynchronizationInterceptor.register(EntitySynchronizationInterceptor.java:160) at org.jboss.ejb.plugins.EntitySynchronizationInterceptor.invokeHome(EntitySynchronizationInterceptor.java:218)

That stacktrace indicates that something before this "register" cause a transaction abort and the EntitySynchronizationInterceptor is trying to register to an aborted transaction. You'll have to track down why the transaction has been aborted.